In our co-pending application there is described a method for disinfecting or sterilizing a surface comprising the steps of:
(1) nebulising a solution comprising a sterilizing agent in a solvent to form a nebulant of finely divided particles of the solution in a gas stream, said solution including a solvent having a lower boiling point than the sterilizing agent;
(2) subjecting the nebulant to energy of a kind and for a duration sufficient to vaporize solvent in preference to sterilizing agent, whereby to increase the concentration of the agent in the nebulant particles;
(3) removing solvent vaporized in step 2 from the gas stream at or above atmospheric pressure and, if necessary, cooling the nebulant to below 70° C.; and
(4) exposing said surface to nebulant from step 3 for a time sufficient to sterilize the surface.
Major advantages of that process are that it avoids (a) the need for vacuum which is associated with prior art commercial vapour processes, (b) the need for a rinsing step associated with prior art commercial solution processes and (c) the need for temperatures above 60° C. which are damaging to many materials, and (d) it is more effective than prior art nebulant and vapour processes especially when treating occluded, mated and lumen surfaces. In preferred embodiments it uses hydrogen peroxide at concentrations which are not classified as skin irritants and which are safe to transport and handle (unlike commercial vapour and plasma processes which use corrosive and irritating 60% peroxide solutions requiring special packaging and handling precautions). The prior art is comprehensively discussed in our co-pending application.
We have now discovered that at least some of the benefits produced by the method of our co-pending application can be achieved simply by alternative means with some surprising additional and unexpected advantages.
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
The present invention arose from the need to find a method to sterilize diagnostic ultrasound (“DU”) probes. These instruments are used for a variety of intra cavity procedures including intra rectal, intra vaginal and oesophageal examination and should be sterilized to prevent cross-infection. The instruments are temperature sensitive and cannot be heated above 55-60° C. Several different plastics may be used in their external construction which may involve joined or mated parts. DU Probes have electrical connectors which are sensitive to corrosion. Often procedures are of short duration but sterilization can take much longer than a procedure, therefore a multiplicity of instruments is needed to enable procedures to be undertaken during long sterilization cycles. Each instrument is expensive and the need for multiple instruments adds greatly to the cost of examinations. Moreover, the procedures are often performed in locations where there is no access to centralized or specialized sterilization equipment such as plasma sterilizers which employ high vacuum and cost upwards of $100,000. At present DU probes are commonly disinfected using high level disinfectants such as liquid glutaraldehyde or OPA (ortho phthalyl aldehyde) both of which are associated with a high Occupational Health and Safety risk as well as a risk to patients from residues. Currently no sterilization procedure is available for these instruments and high level disinfection is not considered entirely satisfactory by health professionals using these instruments. It will be understood that the invention is not limited to use for sterilizing DU probes and may be used for disinfecting or sterilizing other articles or surfaces. Furthermore, DU probes are not generally stored in a sterile environment and best practice requires that in such cases they be re-disinfected immediately prior to use.
Cummins U.S. Pat. No. 4,744,951 describes a process in which hydrogen peroxide is vapourized and concentrated in a first chamber by means of heat and pressure reduction. (eg 0.01 atms) Water vapour is withdrawn in preference to hydrogen peroxide vapour through a vacuum pump. The thus concentrated peroxide vapour is then admitted to an evacuated sterilization chamber in which it is allowed to contact an article to be sterilized. The process suffers from the major disadvantages that are associated with the need for a vacuum system and evacuation.